The relatively prolonged course of most pain crises—which typically involves increasing intensity of pain and often development of new areas of pain over the first few days—suggests that treatment during the early phases of a crisis might be effective in ameliorating the course of the episode, resulting not only in decreased acute morbidity but possibly also in less long-term tissue damage. The study hypothesis is that administration of abciximab early in the course of a vaso-occlusive sickle cell pain crisis will reduce the median length of hospitalization without an accompanying increase in bleeding or other serious complications.